Joining process

ABSTRACT

A process for the fluxless soldering of aluminum-containing workpieces in substantially non-oxidizing atmospheres is carried out with a solder which contains 2-45% by weight of Al and at least one additive from the group consisting of Bi Sr, Ba, Sb and Be, the balance being Zn. The additives Bi, Sr, Ba and Sb constitute 0.01-10% by weight and the additive Be constitutes 0.00001-1.0% by weight of the solder. These additives lower the viscosity and surface tension of the molten solder and also decrease the interfacial tension between the molten solder and the workpieces.

United States Patent Schoer et a1.

Filed:

JOINING PROCESS Inventors: Heinz Schoer, Alfter; Werner Schultze, Bonn, both of Germany Assignee: Vereinigte Aluminium-Werke Aktiengesellschaft, Bonn, Germany Aug. 29, 1972 Appl. No.: 285,099

Related US. Application Data Continuation-impart of Ser. No. 98,173, Dec. 14,

1970, abandoned.

Sept. 2, 1971 Foreign Application Priority Data Germany 2143966 US. Cl. 29/494, 29/504, 75/178 A Int. Cl B23k 31/02, B23k 35/38 Field of Search 75/178 A, 178 R, 178 AC,

75/178 AT, 178 AM, 178 AN; 29/494, 504

References Cited UNITED STATES PATENTS Baldwin et a1. 75/178 A Richardson 75/178 A Hodge et a1. 29/504 X Martin 29/494 Schwartz et a1, 29/494 Apr. 30, 1974 3,480,465 11/1969 lmabayashi et al. 1 17/71 FOREIGN PATENTS OR APPLICATIONS 24,209 12/1961 Japan 29/504 OTHER PUBLICATIONS Abstract of Application Ser. No. 740,715 filed Apr. 10, 1947, published July 26, 1949. Welding Handbook", Section 4, 5th Edition, published in 1966 by American Welding Society, pp. 69-120, 69.126. Technical Library.

Primary ExaminerJ. Spencer Overholser Assistant Examiner-Ronald J. Shore Attorney, Agent, or FirmMichael S. Striker [57] ABSTRACT 9 Claims, No Drawings JOINING PROCESS CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of our application Ser. No. 98,173 filed Dec. 14, 1970 and entitled Process and Solder for Soldering Aluminumcontaining workpieces, now abandoned.

BACKGROUND OF THE INVENTION An intrinsic problem exists in the soldering of aluminum or aluminum alloy workpieces as a result of the very cohesive, ever present oxide film on the surfaces of these workpieces. The problem lies in the fact that the oxide film prevents the surfaces of the workpieces from being adequately wetted by the molten solder. Although the oxide film is very thin, it is, however, impervious and stable and reforms spontaneously after being removed, for example, by corrosive means. Furthermore, the oxide film is strengthened during the soldering processes inasmuch as these processes are carried out in oxidizing atmospheres such as air, for example. Thus, aside from the special methods of friction and ultrasonic soldering, it has, until now, been necessary in the soldering of aluminum to remove the oxide film from the area of the joint by using fluxes. In addition, the area to be soldered has to be protected in order to prevent renewed oxidation. The fluxes used are composed, in part, of metallic salts such as, for example, zinc salts, which cause metallic deposition to occur in the area of the joint and which, as a consequence, lead to an improvement in the wetting characteristics of the solder.

Fluxes suitable for the soldering of aluminum generally contain chlorides or fluorides and, for the purpose of soft soldering, may also contain pure organic compounds. However, all fluxes possess the disadvantage of being corrosive, most of them extremely so, and, as a result, their residues must be removed after soldering. In addition, there is the danger of the flux being incorporated into the soldered joint. The incorporated flux and the flux residues greatly impair the corrosion resistance of the soldered article especially when moisture comes into contact with the soldered joint. The removal of the flux residues is expensive and, additionally, is usually incomplete.

A solder for aluminum and aluminum alloys is already known from German Pat. No. 896,444 issued in 1941. This solder is composed of high-grade zinc and high-purity aluminum and may contain, in additionto other alloying elements, up to l% Sb and/or up to 1% Bi. However, the sate of the art at that time was such, that the use of a flux in conjunction with such solders was considered indispensable. This is also shown by British Pat. No. 747,813 issued in 1951-1952. In the latter patent it is indicated that the use of zincaluminum solders requires the simultaneous utilization of special fluxes containing metallic salt additions.

It is clear from the above that fluxless soldering, heretofore considered impossible, would provide great technical and economic advantages.

SUMMARY or THE INVENTION It is, accordingly, an object of the present invention to overcome the disadvantages of the prior art.

More particularly, it is an object of the present invention to provide a process for the soldering of aluminum or aluminum alloys which does not possess the above disadvantages.

A more specific object of the present invention is to provide a process for the fluxless soldering of aluminum or aluminum alloys.

Another object of the present invention is to provide a process for the fluxless soldering in an at least substantially non-oxidizing atmosphere of aluminum or aluminum alloys.

Some of the novel features of the present invention thus reside in-a process for the fluxless soldering of aluminum-containing workpieces in substantially nonoxidizing atmospheres. The process is carried out with a solder which contains 2-45% by weight of Al and at least one of the additives from the group consisting of Bi, Sr, Ba, Sb and Be, the balance being Zn. The additives Bi, Sr, Ba and Sb constitute 0.0ll0% by weight and the additive Be constitutes 0.00001-1 .0% by weight of the solder. These additives lower the viscosity and surface tension of the molten solder and also decrease the interfacial tension between the molten solder and the workpieces.

The present invention thus provides a material consisting primarily of Zn and containing additions of Bi, and/or Sr, and/or Ba, and/or Sb, and/or Be, as well as Al. The Bi, Sr, Ba and Sb additions constitute 0.01-10% by weight of the material and are preferably present in amounts of O .O5-2.0% by weight. On the other hand, the Be addition constitutes 0.0000l-l.0% by weight of the material and is preferably present in amounts of 0.0002-0.1% by weight. The substance of the invention lies in the use of this material as a solder for the soldering of aluminum-containing workpieces in non-oxidizing atmospheres or in an atmosphere wherein the oxygen content in the vicinity of the area to be soldered is low.

No special precautions beyond those normally used in soldering processes are necessary for the fluxless soldering' of aluminum when utilizing the solder provided by the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Tests have shown that solders according to the present invention are, surprisingly, suitable for the fluxless soldering of aluminum when a non-oxidizing atmosphere or an atmosphere of low oxygen content is provided about the area to be soldered. An inert protective gas for soldering such as, for example, welding grade argon, commercial quality nitrogen, forming gas or ammonia, may be used for providing the non-oxidizing atmosphere. A low vacuum of, say, 10" to 10 torr may also be used for this purpose.

These tests have also surprisingly shown that the incorporation of the above-mentioned additions in the solder not only lowers the viscosity and surface tension of the molten solder but, simultaneously, substantially reduces the interfacial tension between the molten solder and the workpieces. As a result, the wetting characteristics of the solder are significantly improved.

A distinction can be made between soft and hard zinc-aluminum solders on the basis of composition and, as a consequence, on the basis of soldering temperature. Solders in accordance with the present invention containing the above-mentioned additions and substantially 2-26% by weight of A1 with the balance being Zn are classified as soft solders. On the other hand, solders according to the present invention containing the above-mentioned additions with more than 26% by weight and up to 45% by weight of Al and, if required, an additional alloy constituent of up to 1% by weight of Mn with the remainder being Zn, are classified as hard solders. These solders can be utilized in all conventional forms such as, for example, wires, bars, formed shapes, foils, solder-plated sheets etc. The term hard solders used here is intended to denote brazing alloys.

The following are examples of solder compositions in accordance with the present invention.

EXAMPLE 1 EXAMPLE 2 Element by Element by weight weight Zn 94.80 Zn 95.19 Al 4.18 A1 4.55 Be 0.06 Bi 0.16 Mn 0.86 Be 0.02 Impurities 0.10 Impurities 0.08

EXAMPLE 3 EXAMPLE 4 Element by Element by weight weight Zn 67.15 Zn 59.63 AI 32.73 A1 39.88 Be 0.09 Bi 0.06 Impurities 0.03 Be 0.01 Mn 0.37 Impurities 0.05

The above examples are in no way intended to limit the scope of the present invention but serve merely to illustrate the preferred embodiments. The solder compositions may be varied as necessary to suit particular requirements.

The soldering tests were carried out in an electrically heated oven. Pure aluminum and aluminummanganese sheets were used in conjunction with solders having compositions as outlined in the above examples. These tests, which in accordance with the present invention were performed without a flux, were carried out in a protective gas'atmosphere such as, for example, argon and nitrogen. For solders having compositions as in examples 1 and 2 (soft solders), the soldering temperature was between 400 and 415 C whereas for solders having compositions as in examples 3 and 4 (hard solders), the soldering temperature was between 530 and 545 C. Soldering times were of the order of 2 minutes. Satisfactory soldered joints were produced in all of the above tests.

In contrast, the commercial zinc-aluminum 4 solder without the above-mentioned additions did not produce a joint when no flux was used.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of joining methods differing from the types described above.

While the invention has been illustrated and described as embodied in solder for the fluxless soldering of aluminum-containing workpieces in a substantially non-oxidizing atmosphere, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential I characteristics of the generic or specific aspects of this invention and, therefore such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended.

1. In a process of brazing; aluminumcontaining workpieces, the step of brazing said workpieces with a filler metal consisting essentially of 2645% by weight of Al, up to about 1% by weight of Mn, and 0.0000ll.0% by weight of Be, the remainder being substantially Zn, said Be lowering the viscosity and surfacetension of said filler metal in its molten state and substantially decreasing the interfacial tension between the molten filler metal and said workpieces, and said step being performed without a flux and in a substantially non-oxidizing atmosphere.

2. In a process as defined in claim 1, wherein said filler metal contains 0002-0. 1% by weight of Be.

3. In a process of brazing aluminum-containing workpieces, the step of brazing said workpieces with a filler metal consisting essentially of 2645% by weight of Al, up to about 1% by weight of Mn, 0.0000l-1.0% by weight of Be, and 0.01-l0% by weight of at least one substance selected from the group consisting of Bi, Sr, Ba and Sb, the remainder being substantially Zn, said Bi, Sr, Ba, Sb and Be lowering the viscosity and surface tension of said filler metal in its molten state and substantially decreasing the interfacial tension between the molten filler metal and said workpieces, and said step being performed without a flux and in a substantially non-oxidizing atmosphere.

4. In a process as defined in claim 3, wherein said filler metal contains 0.05-2% by weight of said at least one substance.

5 In a process as defined in claim 3, wherein said filler metal contains 0.0020.l% by weight of Be.

6. In a process as defined in claim 1, wherein said filler metal contains 32.73% by weight of Al, 0.09% by weight of Be, and 0.03% by weight of impurities.

7. In a process of soldering aluminum-containing workpieces, the step of soldering said workpieces with a solder consisting essentially of 4.18% by weight of Al, 0.06% by weight of Be, 0.86% by weight of Mn, and 0.10% by weight of impurities, the remainder being substantially Zn, said Be lowering the viscosity and surface tension of said-solder in its molten state and substantially decreasing the interfacial tension between the molten solder and said workpieces.

8. In a process of soldering aluminum-containing workpieces, the step of soldering said workpieces with a solder consisting essentially of 4.55% by weight of Al, 0.16% by weight of Bi, 0.02% by weight of Be, and 0.08% by weight of impurities, the remainder being substantially Zn, said Be and Bi lowering the viscosity and surface tension of said solder in its molten state and substantially decreasing the interfacial tension between the molten solder and said workpieces.

9. In a process of brazing aluminum-containing workpieces, the step of brazing said workpieces with a brazing alloy consisting essentially of 39.88% by weight of Al, 0.06% by weight of Bi, 0.01% by weight of Be, 0.37% by weight of Mn, and 0.05% by weight of impurities, the remainder being substantially Zn, said Be and Bi lowering the viscosity and surface tension of said brazing alloy in its molten state and substantially decreasing the interfacial tension between the molten solder and said workpieces. 

2. In a process as defined in claim 1, wherein said filler metal contains 0.002-0.1% by weight of Be.
 3. In a process of brazing aluminum-containing workpieces, the step of brazing said workpieces with a filler metal consisting essentially of 26-45% by weight of Al, up to about 1% by weight of Mn, 0.00001-1.0% by weight of Be, and 0.01-10% by weight of at least one substance selected from the group consisting of Bi, Sr, Ba and Sb, the remainder being substantially Zn, said Bi, Sr, Ba, Sb and Be lowering the viscosity and surface tension of said filler metal in its molten state and substantially decreasing the interfacial tension between the molten filler metal and said workpieces, and said step being performed without a flux and in a substantially non-oxidizing atmosphere.
 4. In a process as defined in claim 3, wherein said filler metal contains 0.05-2% by weight of said at least one substance.
 5. In a process as defined in claim 3, wherein said filler metal contains 0.002-0.1% by weight of Be.
 6. In a process as defined in claim 1, wherein said filler metal contains 32.73% by weight of Al, 0.09% by weight of Be, and 0.03% by weight of impurities.
 7. In a process of soldering aluminum-containing workpieces, the step of soldering said workpieces with a solder consisting essentially of 4.18% by weight of Al, 0.06% by weight of Be, 0.86% by weight of Mn, and 0.10% by weight of impurities, the remainder being substantially Zn, said Be lowering the viscosity and surface tension of said solder in its molten state and substantially decreasing the interfacial tension between the molten solder and said workpieces.
 8. In a process of soldering aluminum-containing workpieces, the step of soldering said workpieces with a solder consisting essentially of 4.55% by weight of Al, 0.16% by weight of Bi, 0.02% by weight of Be, and 0.08% by weight of impurities, the remainder being substantially Zn, said Be and Bi lowering the viscosity and surface tension of said solder in its molten state and substantially decreasing the interfacial tension between the molten solder and said workpieces.
 9. In a process of brazing aluminum-containing workpieces, the step of brazing said workpieces with a brazing alloy consisting essentially of 39.88% by weight of Al, 0.06% by weight of Bi, 0.01% by weight of Be, 0.37% by weight of Mn, and 0.05% by weight of impurities, the remainder being substantially Zn, said Be and Bi lowering the viscosity and surface tension of said brazing alloy in its molten state and substantially decreasing the interfacial tension between the molten solder and said workpieces. 